The invention relates to a drive for a printing press with a plurality of printing units and, more particularly, wherein the printing units are mechanically interconnected through the intermediary of a gear train and are associated, respectively, with a drive motor, the drive motors supplying power to the gear train at a preset torque ratio.
In the printing field, demands are continuously being made both in the direction of rationalization and also in the direction of quality improvement. In order to produce high-quality multi-color prints which have been printed on both sides and possibly also varnished in one passage through the printing press, it is necessary, particularly with respect to sheet-fed printing, to dispose a multiplicity of printing units one behind the other. These printing units must be matched to one another to a high degree with regard to the mode of operation thereof.
In order to achieve a reduction in the loading of the gear train, it is customary to employ multiple drives in the case of a printing press with a plurality of printing units, i.e., a plurality of drive motors are provided which supply power to the gear train at various locations thereof.
It is important, in this respect, that there should be a constant power flow in the gear train throughout the entire printing process. Because a constant power flow causes a constant bracing effect in the gearwheel train, in-register maintenance is thereby assured. Should the power flow in the gearwheel train change due to differences in loading, then uncontrollable bracings or stresses occur in the gearwheels, which are considered to be elastic. Low-frequency vibrations are excited and. have an adverse effect upon the quality of the printed products in the form of ghosting or register errors. Such printing errors normally lead to the printing of waste.
In order to counteract a change in direction of the power flow in the gear train of a printing press, the drive motors conventionally supply the power to the gear train at a preset torque ratio. Although such a measure ensures a constant contact of gear flanks or sides in the gear train, it is not capable of suppressing variations in bracings or stresses in the gearwheel train when changes in loading and speed occur. Register errors caused by a change in the power flow as a result of the inconstant, i.e. variable bracings or stresses are conventionally corrected by the pressman or machine operator through the use of register crosses, or automatically through the intermediary of a mechanical register adjustment in the longitudinal direction of the sheets which are being processed.
It is accordingly an object of the invention to provide a drive for a printing press with a plurality of printing units which is of such construction as to automatically minimize register errors between the individual printing units automatically.
It is accordingly a conceptual part of the invention to provide a synchronizing drive arrangement for a printing press composed of multiple printing units, which has a gearwheel train inter-connecting the printing units, and which in addition has means for introducing a controlled torque bias at several points of the gearwheel train.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a drive for a printing press with a plurality of printing units mechanically interconnected through the intermediary of a gear train, the printing units being associated with respective drive motors for supplying power to the gear train in a preset torque ratio, comprising a control device, means for supplying to the control device information regarding printing-specific variables, the control device having means for determining, from the printing-specific variables, load-torque changes in the printing units, individually, and for energizing the drive motors so that power flow in the gear train is constant when averaged over time.
In accordance with another feature of the invention, the drive includes a memory operatively associated with the control device and having stored therein characteristic curves for determining load-torque changes as a function of the respective printing-specific variables, as the variables apply individually for each printing unit. Such characteristic curves are determined experimentally, for example in test runs of the printing machine.
In accordance with an alternative feature of the invention, the control device comprises a computing device for computing, through the intermediary of the printing-specific variables, or through changes therein, the load-torque changes occurring in a respective printing unit.
In accordance with an added feature of the invention, the control device has means for compensating for the load-torque change occurring in a respective printing unit by applying to the corresponding drive motor a corresponding change in driving torque, which has been stored in memory or computed.
In accordance with an additional feature of the invention, one of the printing-specific variables is the rotational speed of the printing press.
In accordance with yet another feature of the invention, one of the printing-specific variables is the viscosity of the printing ink in the respective printing units, individually related to the respective printing unit.
In accordance with yet a further feature of the invention, one of the printing-specific variables is the ink distribution in the respective printing units, individually related to the respective printing unit.
In accordance with a concomitant feature of the invention, one of the printing-specific variables is the temperature of at least one of the inking and dampening units in the respective printing units, individually related to the respective printing unit.
Amongst those printing-specific variables which affect the load torque, the press speed, i.e., the rotational speed of the printing press, is of primary significance. The further influencing variables are the viscosity of the printing ink, which may vary, for example, from printing unit to printing unit, the ink distribution in the individual printing units, determination of which is possible, for example, through the positions of the ink keys, and the temperature of the inking-unit and/or dampening unit, the temperature of the inking unit having a by no means insignificant influence on the viscosity of the ink and therefore also on the load torque of the corresponding printing unit.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a drive for a printing press with a plurality of printing units, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which: